Bump vls from 0.5.6 to 0.5.7 in /server (#88)

Bumps [vls](https://github.com/vuejs/vetur) from 0.5.6 to 0.5.7.
- [Release notes](https://github.com/vuejs/vetur/releases)
- [Changelog](https://github.com/vuejs/vetur/blob/master/CHANGELOG.md)
- [Commits](https://github.com/vuejs/vetur/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>